Inorganic Photorefractive Materials

Light-induced refractive index changes — so-called photorefractive effects — in inorganic electro-optic crystals were discovered by Ashkin et al. in 1966 [1]. Though in the beginning these effects seemed to be very undesirable (“optical damage”), Chen et al. recognized only two years later the significance for holographic data storage [2]. In 1975, Staebler et al. reported the recording of 500 thermally fixed volume phase holograms in LiNbO3:Fe, each hologram with more than 2.5% readout efficiency [3] . The method is based on the Bragg condition allowing the superposition of many volume (“thick”) holograms at the same site under different angles.